Sure, go into the settings menu of the Yahoo app by tapping the three bars at the top left of the screen (settings is at the bottom of the list on the left side pop out), tap account settings then tap other and turn off 'use signature'.

Sure, go into the settings menu of the Yahoo app by tapping the three bars at the top left of the screen (settings is at the bottom of the list on the left side pop out), tap account settings then tap other and turn off 'use signature'.